The present invention is related with an application of a novel method available to release energy stored in stimulable phosphors, coated in storage phosphor panels. So the present invention relates to a device essentially providing particular storage phosphors as composite compounds having the ability to absorb and to store part of absorbed X-ray and/or UV-ray energy and to emit part of it again under stimulating forces in form of (visible) detectable light energy. This invention also relates to a method of recording and reproducing said energy, pattern-wise where desired, by means of a screen or panel containing such phosphors and built in in the said device.
Well-known in diagnostic imaging is the use of phosphors in the production of X-ray images. In a conventional radiographic system an X-ray radiographic image is obtained by X-rays transmitted imagewise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) wherein phosphor particles absorb transmitted X-rays and convert them into visible light and/or ultraviolet radiation. As silver halide grains or crystals, present in emulsions coated in layers of a silver halide photographic film material are more sensitive to the thus converted X-ray energy than to direct impact of X-rays (due to a less effective absorption of those energetic X-rays) the said conversion is in favour of image formation on the film material.
According to another method of recording and reproducing an X-ray pattern disclosed e.g. in U.S. Pat. No. 3,859,527 a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel is exposed to incident pattern-wise modulated X-rays and as a result thereof temporarily stores energy contained in the X-ray radiation pattern. At some interval after the exposure, a beam of visible or infra-red light scans the panel in order to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which can be processed in order to produce a visible image. For this purpose, the phosphor should store or accumulate as much as possible of the incident X-ray energy and emit an amount of the stored energy as low as possible before stimulation by the scanning beam. This form of radiography, wherein use is made of storage phosphor screens or panels, also called stimulable phosphor panels or accumulation phosphor panels is called xe2x80x9cdigital radiographyxe2x80x9d or xe2x80x9ccomputed radiographyxe2x80x9d.
Use of alkali metal halide phosphors in storage screens or panels is well known in the art of storage phosphor radiology, wherein at least part of the energy contained in an X-ray pattern is temporarily stored. The high crystal symmetry of these phosphors makes it possible to provide structured screens and binderless screens, in favour of image quality. Examples of such alkali metal phosphor can be found in several documents. In e.g. U.S. Pat. No. 5,028,509 a phosphor corresponding to general formula
(M1xe2x88x92x. M1X)X.aM2+Xxe2x80x22. bM3+Xxe2x80x33:dB,
wherein M is Cs or Rb, Mxe2x80x2 is at least one metal selected from the group consisting of Li, Na, K, Rb, and Cs, M2+ is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, M3+ is at least one metal selected from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; X, Xxe2x80x2 and Xxe2x80x3 may be the same or different and each of them represents a halogen atom selected from the group consisting of F, Br, Cl, I provided that all Xxe2x80x2 atoms are the same, B is an element selected from the group consisting of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu, Mg, Pb, Bi, Mn, and In. 0 less than x less than 1 en 0 less than a less than 1 en 0 less than b less than 0.5 en 0 less than d less than 0.2
In U.S. Pat. No. 5,055,681 a binderless screen comprising the phosphor as disclosed in U.S. Pat. No. 5,028,509 has been disclosed. In U.S. Pat. No. 4,806,757 a CsI phosphor has been disclosed, comprising between 0.0001 to 1 mole % of at least one element selected from the group consisting of Li, K, Rb, Cu, Au, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, B, Al, Ga, In, Tl, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Si, Ti, Zr, Ge, Sn, Pb, As, Sb and Bi.
Alkali metal halide phosphors performing as desired qualities absorption characteristics, speed, storage capabilities etc. have been disclosed in EP-A 0 751 200, wherein besides high speed also high chemical stability and low sensitivity to humidity have been appreciated as well as ability to produce screens comprising vapour deposited phosphor layers providing high image definition.
The radiation image storage phosphor screen according to that invention comprises an alkali metal halide phosphor characterized in that said phosphor contains a dopant selected from the group consisting of Ga1+, Ge2+, Sn2+, Sb3+ and As3+. In a preferred embodiment thereof the alkali metal is Cs and/or Rb.
In order to provide a method for recording X-rays following steps were recommended:
(i) exposing the photostimulable storage phosphor screen, comprising novel alkali metal halide phosphors,
(ii) stimulating said photostimulable screen in order to release the stored X-ray energy as stimulated light and
(iii) collecting said stimulated light.
In order to release energy stored by a stimulable phosphor use has hitherto often been made of optical light sources as mentioned hereinbefore. As a consequence thereof optical filters are required in order to separate light emitted by the storage phosphors after stimulation and light originating from the stimulation source. In order to develop a scan-head in order to scan a plate or panel built-up with stimulable phosphors in order to release said stored energy, it is recommended to reduce the volume of such a scan-head to a minimum. Especially when the detector, collecting said stimulated light is a CCD with Fiber Optic Plate (FOP), the image plate should be placed in direct contact with this fiber optic plate in order to obtain a sufficiently good resolution. Presence of any additional intermediate layer, as e.g. a filter layer, may lay burden thereupon and any measure in order to simplify the process of reading out a storage phosphor is welcome as well as any development in form of a practically useful device as a spin-off therefrom.
Therefore it is an object of the present invention to provide one or more device(s) offering an easy method in order to stimulate storage phosphors, wherein said device is essentially provided with panels built up with such storage phosphors.
It is a further object of the present invention to extrapolate said method in order to provide practically useful devices as a spin-off thereof.
Any other object will become apparent from the description hereinafter.
A device for measuring a pressure force or changes thereof (directly or indirectly) applied by a pressure source differing from a direct air pressure energy source and for reading out said pressure force, has been provided as a spin-off from the property of xe2x80x9ctribostimulabilityxe2x80x9d of storage phosphors, wherein said device essentially comprises a (tribo)stimulable storage phosphor sheet or panel and means in order to apply said pressure force onto said stimulable storage phosphor sheet or panel and wherein said pressure source and said storage phosphor panel are positioned relative to each other (with or without intermediate means) so that pressure or variations thereof caused or generated (directly or indirectly) by said pressure source reach said stimulable phosphor, also called tribostimulable phosphor, thereby stimulating said phosphor by pressure in order to release tribostimulated light, said device further having capturing means to capture said tribostimulated light and detecting means to detect it (and to measure it after detection as a measurable signal).
Because of the proportionality of the emitted light energy with the applied pressure, the technique is suitable for measuring pressure forces and provides methods to do so.